Magnetic recording and reproducing apparatus arranged to save electric power consumed in detecting tape end and reduce load on microprocessor

ABSTRACT

A magnetic recording and reproducing apparatus arranged to use a magnetic tape. The apparatus operates to derive the current taken-up position of the magnetic tape from the signals that are proportional to the rotation frequencies of a capstan motor, a supply reel and a take-up reel. Only when the taken-up position is near the tape end, the apparatus activates LEDs (light emitting elements) for sensing the tape end and photo-transistors (light receiving elements), for sensing the tape end.

This application is a 37 CFR §1.60 continuation of prior applicationSer. No. 08/540,219, filed Oct. 6, 1995 now U.S. Pat. No. 5,699,206,(allowed).

BACKGROUND OF THE INVENTION

The present invention relates to a magnetic recording and reproducingapparatus for recording or reproducing data on a magnetic tape and moreparticularly to the apparatus that is arranged to save an electric powerconsumed in detecting a tape end and reduce a load on a microprocessorprovided in the apparatus.

No light is allowed to pass through a tape on which magnetic substanceis coated or evaporated. Hence, the magnetic recording and reproducingapparatus according to the prior art has arranged to use a magnetic tapehaving a light-transmittable, transparent area (called a leader tape) onthe end of the tape. That is, the apparatus provides a light emittingcircuit and a light receiving circuit. In operation, the light emittedby light emitting circuit passes through the light-transmittable areaand is sensed by the light receiving circuit for detecting the ends ofthe tape.

As this kind of apparatus, a VTR is described in "Introduction to HomeVTR", edited by Corona Publishing Co., Ltd., 1981, pp. 123 to 133.

SUMMARY OF THE INVENTION

The foregoing prior art, however, needs to actuate the light emittingcircuit for emitting light continuously or periodically (atpredetermined time intervals of time according to the switchingoperation) at all times and actuate the light receiving circuit forreceiving the light, for the purpose of detecting the end of the tape inthe same manner. The prior art is, therefore, disadvantageous in thatboth the light emitting circuit and the light receiving circuit have toconstantly consume an electric power.

Further, the apparatus of the prior art provides an analog-to-digitalconverter (called an AD converter) loaded on a microprocessor, throughwhich an output signal sent from the light receiving circuit isconverted into a digital signal. Based on the digital signal, thepresence or absence of light is determined. To execute this operation,the conventional apparatus is required to periodically operate the ADconverter and a program for analyzing a digital value. This has been acontinuous or periodic burden on the microprocessor.

To overcome this shortcomings, it is an object of the present inventionto provide a recording and reproducing apparatus that is arranged toreduce the power consumption and/or load on a microprocessor provided inthe apparatus.

In carrying out the object, a magnetic recording and reproducingapparatus according to an aspect of the invention provides means forsensing a current taken-up position of a magnetic tape. If the currenttaken-up position sensing means determines that the tape taken-upposition is close to the end of the tape, the light emitting circuit isoperated continuously or at predetermined intervals. If the taken-upposition sensing means determines that the tape taken-up position isdistant or away from the end of the tape, the light emitting circuit ismade inoperative for saving the power consumption of the circuit.

If the taken-up position sensing means determines that the current taretaken-up position is close to the end of the tape, the apparatusoperates to supply electricity to the light receiving circuit. if thetaken-up position sensing means determines that the tape taken-upposition is distant from the end of the tape, the apparatus operates tostop the distribution of electric power (called power distribution) tothe light receiving circuit for saving the power consumption in thecircuit.

Further, in the case of sensing the tape end through a microprocessor byanalyzing the output signal of the light receiving circuit to determinethe presence or the absence of passed light on the analyzed result, ifthe taken-up position sensing means determines that the current tapetaken-up position is close to the tape end, the microprocessor isenabled for analyzing the received-light signal. If the taken-upposition sensing means determines that the current tape taken-upposition is distant from the tape end, the analyzing operation of thereceived-light signal is stopped for reducing the load on themicroprocessor.

As described above, the magnetic recording and reproducing apparatus ofthe present invention has the foregoing means. Hence, the apparatusenables to turn off the light emitting elements for sensing the tape endand stop the power distribution to the light receiving circuit on mostof the entire tape length while the tape is running. This makes itpossible to greatly save the power consumption. In the case ofapparatuses which use a microprocessor to analyze the received-lightsignal and sense the tape end based on the analyzed result, it becomespossible to stop the analyzing program on most of the entire tape lengthwhile the tape is running, thereby greatly reducing the load on themicroprocessor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a construction of a tape running systemincluded in a magnetic recording and reproducing apparatus according toan embodiment of the present invention;

FIG. 2 is a block diagram showing an arrangement of the magneticrecording and reproducing apparatus shown in FIG. 1;

FIG. 3 is a flowchart (PAD diagram) showing an operating flow of asystem controller included in this embodiment;

FIG. 4 is a view useful for describing the principle of sensing a tapeend, on which the invention is operated;

FIGS. 5A and 5B are views useful for describing the principle of sensinga tape end, on which the invention is operated;

FIG. 6 is a circuit diagram showing a concrete arrangement of a lightemitting circuit included in the embodiment shown in FIG. 2; and

FIG. 7 is a circuit diagram showing a concrete arrangement of a lightreceiving circuit included in the embodiment shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description will be oriented to a magnetic recording and reproducingapparatus according to an embodiment of the present invention withreference to the drawings.

FIG. 1 is a view showing a construction of a tape running systemincluded in the magnetic recording and reproducing apparatus providedwith an optical sensor for sensing a tape end.

The tape running system is constructed to have a head drum 1 on which arotary head is mounted, a capstan motor 2 for running a tape, a capstanshaft 3, a pinch roller 4 on which the tape is running against thecapstan shaft 3, a drum motor 5, the magnetic tape 6 having alight-transmittable area (called a leader tape) on both ends of thetape, tape guide pins 7, 8, 9, 10 for properly changing the direction ofthe tape, a tension pin 11 for keeping tape tension right, an impedanceroller 12 for suppressing tape vibrations, a cassette half 13, a supplyreel 14, a take-up reel 15, a supply reel gear 16, a take-up reel gear17, a light emitting element (LED) 18, and light receiving circuits 19and 20 for sensing a tape end, namely, circuits operating to sense lightpassed through the leader tape.

Next, the description will be oriented to the operation of the taperunning system included in this embodiment with reference to FIGS. 1, 4,5A and 5B.

The principle on which the tape end is sensed will be described withreference to FIG. 4.

As illustrated in FIG. 4, when the tape running is started, thefollowing relation (1) is established among a tape running speed aroundthe capstan shaft of the capstan motor, the tape running speed aroundthe supply reel for supplying the tape, and a tape running speed aroundthe take-up reel for taking up the tape, because those running speedsare equal to each other. ##EQU1## where V denotes a tape speed, R_(c)denotes a radius of the capstan shaft, T_(c) denotes a rotation periodof the capstan motor, Rs denotes a radius of the supply reel containingthe tape, T_(s) denotes a rotation period of the supply reel, R_(t)denotes a radius of the take-up reel, and Tt denotes a rotation periodof the take-up reel.

To derive R_(s) and R_(t) from this relation, the following relation (2)can be obtained. ##EQU2##

The rotation periods of the supply reel and the take-up reel are derivedfrom signals (R-FG signal) that are proportional to the rotationfrequencies of the supply reel and the take-up reel, respectively. Therotation frequency of the capstan motor is derived from a signal (C-FGsignal) that is proportional to the rotation period of the capstanmotor. For example, the input time of the S-Reel FG signal shown in FIG.1 is sequentially measured by the microprocessor. The intervals betweenthe adjacent inputted times are calculated for obtaining a periodproportional to the rotation period of the supply reel. Likewise, theperiod that is proportional to the rotation period or the take-up reelis derived from the T-Reel FG signal. The period that is proportional tothe rotation period of the capstan motor is derived from the C-FGsignal. Since the radius R_(c) of the capstan shaft is predetermined,the radii of the supply reel and the take-up reel each containing thetape are derived from the expression (2).

When the values of R_(s) and R_(t) derived as described above are closeto the radius Rh of the reel hub, it indicates a high possibility thatthe taken-up position of the tape is close to the tape end. Here, thecurrent taken-up position signifies how much of the tape is taken up orwound around the reel. That is, if the following relation (3) is metwhen the tape is running forward, it means that the tape soon reachesthe end of the tape.

    R.sub.s -R.sub.h <R.sub.d                                  (3)

If the following relation (4) is met when the tape is running reverse,it means that the tape soon reaches the start of the tape.

    R.sub.t -R.sub.h <R.sub.d                                  (4)

where R_(d) denotes a threshold value for determining the tape taken-upposition. In addition, though the foregoing two expressions (3) and (4)have no equal sign, they may contain an equal signal depending onrequirements for setting a threshold value, control hardware orsoftware.

Further, the radius R_(h) of the reel hub does not necessarily take onevalue. For example, for the VHS (Video Home System), as shown in FIGS.5A and 5B, mainly, two radii of the reel hub, that is, a larger one anda smaller one are provided. In this case, the difference between theprojected total areas of the tape shown in FIGS. 5A and 5B is used fordetermining the radius of the reel hub. The remarkable difference of theprojected total areas appears between the smaller reel and the largerreel. The total area Sa of the tape can be obtained by the followingexpression (5)

    S.sub.a =π·R.sub.s.sup.2 +π·R.sub.t.sup.2 -2π·R.sub.h.sup.2                             (5)

where R_(s) and R_(t) are obtained from the expression (2). Bysubstituting R_(s) and R_(t) for the expression (5), the followingexpression (6) can be obtained. ##EQU3##

The right side of the expression (6) is a quadratic function withrespect to the radii of the reel hub. If, therefore, a sum of a squareof the rotation period of the supply reel and a square of the rotationperiod of the take-up reel, as shown in the left side of the expression(6), is larger than a predetermined threshold value H, that is, thefollowing expression (7) is met, it is determined that the reel hub usedis the one having the larger radius. ##EQU4##

As noted above, the radius of the reel hub can also be determined.Hence, R_(s) and R_(t) may be obtained by measuring the values of T_(s),T_(t) and T_(c). If, therefore, the relation of the expression (3) or(4) is met, it is determined that the tape soon reaches the end or thestart end of the tape.

These series of calculations and determinations are executed by a tapetaken-up position calculating unit 41 and a tape end determining unit 41shown in FIG. 2. In response to the signals determined by thecalculating unit and the determining unit, the light emitting elementscontained in a light emitting circuit 18 are turned off except aroundthe end of the tape. Further, by stopping the power distribution to thelight receiving circuits 19 and 20, the power consumption is saved. Thereceived-light signal obtained from the light receiving circuits 19 and20 are read into a microprocessor 34 (see FIG. 2) through an ADconverter 37 (see FIG. 2) for stopping the process for determiningwhether or not the current tape taken-up position reaches the end of thetape. This stoppage serves to reduce the load on the microprocessor.

As described above, the operation of sensing the taken-up position ofthe tape is effective after the magnetic tape is pressed between thepinch roller 4 and the capstan shaft 3 and the tape speeds around thesupply and the take-up reels are synchronized with the tape speed aroundthe capstan shaft. Hence, until the pinch roller is pressed against thecapstan shaft 3 after loading the tape therebetween and the tape runningis started for sensing the exact winding location of the tape, the lightemitting elements are not turned off, the power distribution to thelight receiving circuit is not stopped, and the processing of the outputsignal from the light receiving elements is not stopped. Theseoperations serve to prevent the erroneous operation of the recording andreproducing apparatus.

Next, description will be oriented to a magnetic recording andreproducing apparatus for a video signal according to an embodiment ofthe present invention. FIG. 2 shows an arrangement of the magneticrecording and reproducing apparatus for a video signal.

The magnetic recording and reproducing apparatus is arranged to have abelt 21 for transmitting a driving force of the capstan motor to a reelgear, gears 22, 22', 23 and 24 for transmitting the driving force of thecapstan motor to the reel gear, a recording signal processing circuit 25for mainly modulating a frequency of a recording signal, a reproducingsignal processing circuit 26 or mainly demodulating the reproducedsignal whose frequency is modulated, a switch 27 for switching an inputof a modulating signal for the recording frequency to the rotatingmagnetic heads 28 and 29 or an output of a modulating signal for thereproducing frequency out of those heads, driving circuits 30 and 31 fordriving the head drum motor and the capstan motor, a microprocessor 34,DA converters 35 and 36 for converting a digital signal into an analogsignal, AD converters 37 and 38 for converting an analog signal to adigital signal, a drum servo processing unit 39 for generating arotation control signal of the drum motor, a capstan servo processingunit 40 for generating a rotation control signal of the capstan motor, atape end determining unit 41 for analyzing the output signals sent fromlight receiving circuits 19 and 20 for sensing a tape end anddetermining the tape end based on the analyzed result, a tape taken-upposition sensing unit 42 for deriving an FG signal that is proportionalto a rotation frequency of the supply reel and the take-up reel and anFG signal that is proportional to the rotation frequency of the capstanmotor, an LED control unit 43 for controlling on or off of alight-emitting diode contained in the light emitting circuit 18 based onthe sensed tape taken-up position, a determination signal generatingunit 46 for generating a position determining signal for controlling thepower distribution to the light receiving circuits 19 and 20, and asystem controller 44 for controlling an overall function of theapparatus.

The components 1 to 20 are the same as those of the running system ofthe invention as shown in FIG. 1.

Now, description will be oriented to the operation of the recording andreproducing apparatus according to this embodiment.

In response to a recording or reproducing resuest issued to the system,the system controller 44 operates to instruct the start of the drummotor to the drum servo processing unit 39. Then, the system controller44 operates to instruct the start of the capstan motor to the capstanservo processing unit 40. When the capstan motor is started and the taperunning is started with the tape pressed between the capstan shaft andthe pinch roller, the capstan motor FG signal, the supply reel FG signaland the take-up reel FG signal are output. The tape taken-up positionsensing unit 42 operates to derive the tape taken-up position from thesethree FG signals, based on the foregoing principle.

Until the tape taken-up position is established or determined, the tapetaken-up position sensing unit 42 operates to issue a signal indicatingthat the position is not determined to the LED controller 43, the tapeend determining unit 41, the AD converter 37, and the system controller44. Further, the signal is indicated to the light receiving circuits 19and 20 through a proper output pin provided in the microprocessor. Thisresults in activating all the functions provided in the conventionaltape end sensing continuously or at predetermined intervals. During thisperiod, in response to the indication the LED controller 43 operates toactivate the light-emitting diode contained in the light emittingcircuit 18.

When the tape taken-up position is established or determined, theposition is output to each of the above-mentioned components. If theposition is distant from the tape end, the tape taken-up positionsensing unit 42 turns off the light emitting diode through the LEDcontroller 43 and stops the operations of the AD converter 37 and thetape end determining unit 41 and further stops the power distribution tothe light receiving circuits 19 and 20.

The concrete arrangement of the light emitting circuit 18 containing theLED is illustrated in FIG. 6. In FIG. 6, the determination signalgenerating unit 46 operates to issue the LED control signal to a base ofa transistor 54. In response to an instruction given by the tapetaken-up position sensing unit 42, the LED controller 43 contained inthe microprocessor 34 shown in FIG. 2 operates to control the LEDcontrol signal down to the grounding potential if the taken-up positionis not close to the tape end. This constantly keeps the LED off.Conventionally, the LED control signal output from the microprocessorserves to constantly keep the LED on or off at all times. In contrast,the apparatus according to this embodiment has a function of suppressingthe electric power consumed by the LED if the taken-up position is notclose to the tape end.

Further, a concrete arrangement for stopping the power distribution tothe light receiving circuits 19 and 20 is illustrated in FIG. 7. Thetape taken-up position determination signal (distribution stop signal)supplied by the microprocessor 34 is applied to the bases of transistors52 and 53 contained in the light receiving circuits 19 and 20. If thetape taken-up position is not near the tape end, by controlling thepotential at the bases of the transistors 52 and 53 down to the Vccpotential, the transistors 52 and 53 are cut off so that the powerdistribution to photo transistors 50 and 51 is stopped. In theconventional operation, if the light emitted from the LED contained inthe light receiving circuit 18 shown in FIG. 1 is blocked by the tapeand does not reach the photo transistors 50 and 51, the phototransistors 50 and 51 constantly keep on and consumes the electric powerin response to the light leaked into the VTR set. Hence, the transistors52 and 53 of the present system serve to stop the power distribution, sothat the power consumption of the photo transistors is suppressed.

Moreover, the outputs from the emitters of the photo transistors 50 and51 are applied to an adding circuit 32. The outputs from the collectorsthereof are applied into the AD converter 37 of the microprocessor 34.Conventionally, the microprocessor operates to check the change of theoutput data of the AD converter at all times at periodic intervals anddetermine if the current taken-up position of the tape reaches the tapeend based on the checked result. In constrast, the apparatus of thisembodiment operates to stop these series of operation if the currenttaken-up position is not near the tape end. This results in reducing theprocessing burden of the microprocessor.

The aforementioned process for sensing a tape end is controlled by thesystem controller shown in FIG. 2. The concrete example of the processis shown in FIG. 3. As shown, when the system controller 4 receives acommand of reproduction, recording, rewinding or fast feeding from auser (301), the system controller 4 operates to issue a command to thedrum servo processing unit 39 and the capstan servo processing unit 40as shown in FIG. 2 for starting the drum motor and the capstan motor. Asa result, the tape running is started. Then, until the tape taken-upposition is established or determined (302), the tape taken-up positionis checked (303) and the LED keeps operative and is turned on like theprior art (304). The adding signals output from the light receivingcircuits 19 and 20 are read into the microprocessor 34 through the ADconverter 37. Then, the received-light data, which is converted into adigital signal, is checked at intervals (305) for determining if thecurrent taken-up position is the tape end (306). If it is the tape end,the tape running is stopped (307). Once the tape is stopped, the processfor sensing the tape end is not necessary. Hence, the operation jumps tothe Exit step (308), where the conventional process is terminated forsensing the tape end by determining the taken-up position of the tape.

If the tape is not near the tape end, the operation is executed to turnoff the LED (309) and stop the power distribution to the light receivingcircuit (310). Then, while the tape taken-up position is constantlydetermined (312), the operation waits for when the tape comes closer tothe end or a stopping indication given by the user without having tocheck the received light data from the light receiving circuits 19 and20 (311). If the tape taken-up position sensing process 42 determinesthat the current taken-up position is near the tape end, the LED isturned on (313), the power distribution to the light receiving circuitis restarted (314), and the check for the received light data isstarted. Then, until the taken-up position of the tape comes closer tothe tape end (315), unless the VTR changes its operation in response tothe user's request, the process for sensing the tape end on thereceived-light data is continued (316). If the tape reaches its end(317), the tape running is stopped (318) as noted above. Then, theoperation jumps to the Exit step (319), at which the operation gets outof the process for sensing the tape end.

As noted above, the recording and reproducing apparatus according to thepresent invention operates to stop the operation of the LED for sensingthe tape end and the power distribution to the light receiving elementsexcept that the current taken-up position of the tape is not determinedor is near its end. Hence, the apparatus enables to greatly save thepower consumption and stop the processes for doing an analog-to-digitalconversion of the output signal from the light receiving elements andsensing the tape end, thereby allowing the load on the microprocessor tobe reduced.

As mentioned above, the apparatus according to the present inventionenables to turn off the light emitting elements for sensing the tape endon most of the entire tape length while the tape is running and stop thepower distribution to the light receiving circuit. This makes itpossible to greatly save the power consumption of the apparatus.Further, in the case of apparatuses employing a microcomputer to analyzethe received-light signal and sense the tape end on the analyzed result,the analyzing program is allowed to be stopped on most area of theentire tape length while the tape is running. This also makes itpossible to greatly reduce the load on the microprocessor.

What is claimed is:
 1. A magnetic recording and reproducing apparatus for use with a magnetic tape having a light transmittable area on an end of said magnetic tape, comprising;light emitting means for emitting a light to illuminate said magnetic tape; light receiving means for sensing a light emission from said light emitting means to recognize the end of said magnetic tape when a taken-up position of said magnetic tape is the end of said tape; means for controlling light emissionlextinction of said light emitting means; a head drum having a rotary head mounted thereon: means for winding said magnetic tape on said rotary drum; means for traveling said magnetic tape; wherein at least one of light emission intervals and light extinction intervals during a period from a time before said means for winding starts to wind said magnetic tape on said rotary head till said means for winding has finished winding is different from at least one of light emission intervals and light extinction intervals when said tape runs or travels after said magnetic tape is wound on the rotary drum.
 2. A magnetic recording and reproducing apparatus for use with a magnetic tape having a light transmittable area on an end of said magnetic tape, comprising:light emitting means for emitting a light to illuminate said magnetic tape; means for sensing a light emission of said light emitting means to recognize a tape end when a tape taken-up position is said tape end; means for controlling light emission/extinction of said light emitting means; a rotary drum having a magnetic head mounted thereon: means for winding said magnetic tape onto said rotary drum; means for traveling said magnetic tape; means for taking-up said magnetic tape; means for supplying said magnetic tape; wherein at least one of light emission intervals and light extinction intervals of said light emitting means when at least one of said tape taking-up means and said tape supplying means is deviated from an associated one of respective predetermined revolution speeds which vary in accordance with current tape taken-up position, are different from at least one of light emission intervals and light extinction intervals of said light emitting means when both said tape taldng-up means and tape supplying means are at the respective predetermined revolution speeds at current tape taken-up position.
 3. The apparatus of claim 2, wherein said respective predetermined revolution speeds at current tape taken-up position are respective revolution speeds of said tape taking-up means and said tape supplying means at current taken-up position at a recording tape speed or at a substantially the same tape speed as the recording tape speed.
 4. A magnetic recording and reproducing apparatus for use with a magnetic tape having a light transmittable area on an end of said magnetic tape, comprising:a light emitter emitting a light through said magnetic tape; a light receiver sensing a light emission from said light emitting means to recognize the end of said magnetic tape when a taken-up position of said magnetic tape is the end of said tape; a light controller controlling light emission/extinction of said light emitter; a head drum having a rotary head mounted thereon: a winder winding said magnetic tape on said rotary drum; a tape driver for traveling said magnetic tape; wherein at least one of light emission intervals and light extinction intervals during a period from a time before said winder starts to wind said magnetic tape on said rotary head till said winder has finished winding is different from at least one of light emission intervals and light extinction intervals when said tape runs or travels after said magnetic tape is wound on the rotary drum.
 5. A magnetic recording and reproducing apparatus for use with a magnetic tape having a light transmittable area on an end of said magnetic tape, comprising:a light emitter emitting a light through said magnetic tape; a light receiver sensing a light emission of said light emitter means to recognize a tape end when a tape taken-up position is said tape end; a light controller controlling light emission/extinction of said light emitter; a rotary drum having a magnetic head mounted thereon: a winder for winding said magnetic tape onto said rotary drum; a tape driver for traveling said magnetic tape; a tape take-up for taking-up said magnetic tape; a tape supplier for supplying said magnetic tape; wherein at least one of light emission intervals and light extinction intervals of said light emitter when at least one of said tape take-up and said tape supplier is deviated from an associated one of respective predetermined revolution speeds which vary in accordance with current tape taken-up position, are different from at least one of light emission intervals and light extinction intervals of said light emitter when both said tape take-up means and tape supplier means are at [predetermined revolution speeds] the respective predetermined revolution speeds at current tape taken-up position.
 6. A magnetic recording and reproducing apparatus for use with a magnetic tape having a light transmittable area on an end of said tape, comprising:light emitting means for emitting a light to illuminate said magnetic tape; light receiving means for sensing a light emission from said light emitting means to recognize a tape end when a taken-up position of said tape is the end of said tape; means for controlling light emission/extinction of said light emitting means; a rotary drum having a magnetic head mounted thereon; means for winding said magnetic tape onto said rotary drum; means for traveling said magnetic tape by pinching said magnetic tape by pinching said magnetic tape with a driving axis and a rotatable member, wherein at least one of said driving axis and rotatable member has a movable mechanism to switch between pinching and non-pinching of said magnetic tape and at least one of light emission intervals and light extinction intervals of said light emitting means during a period from a tape non-pinching state till the tape reaches a predetermined traveling speed after the tape is pinched through said movable member are different from at least one of light emission intervals and light extinction intervals of said light emitting means when said magnetic tape is traveling at said predetermined speed by said means for traveling. 